1. Field of the Invention
The present invention relates generally to a turntable assembly for optical disks and, more particularly, to a height-variable type turntable assembly, which can adjust the height of a turntable to adjust the working distance between an object lens and an optical disk according to the type of an optical disk placed on the turntable, and an optical disk device including the same.
2. Description of the Related Art
Optical disks are used as information-recording media, which enable information to be recorded thereon and reproduced therefrom without coming in contact with a head for recording and reproducing information, and enable recording density to be increased.
As for the optical disks enabling information to be recorded thereon and reproduced therefrom, there are, for example, optical disks using phase-change type recording layers in which crystalline and amorphous phases are alternated by the irradiation of laser light.
Information is recorded on such optical disks in such a way as to irradiate laser light, which has been modulated based on an information signal to be recorded, onto information-recording surfaces thereof.
As for the optical disks using the phase-change type recording layers that enable information to be recorded thereon and reproduced therefrom, there are Digital Versatile Disks (DVDs). The DVDs have high recording density compared to conventional Compact Disks (CDs). For example, the CDs are formed to have a track pitch of 1.6 μm, while the DVDs are formed to have a track pitch of 0.74 μm. In addition, Blu-ray Disks (BDs) having a track pitch of 0.3 μm has been recently proposed as a new optical disk.
Such a BD is formed to have recording density higher than those of the conventional CD and DVD, so that an amount of information can be recorded on the BD compared to other optical disks of the same size. In practice, the maximum storage capacities of the CD and the DVD are about 650 MB and 4.7 GB, respectively, while the maximum storage capacity of the BD is about 25 GB.
Information recorded on the information-recording surface of an optical disk is read and reproduced through the following steps. That is, an optical disk is placed on a turntable, the optical disk is rotated together with the turntable by the driving of a spindle motor, and an optical pick-up equipped with an object lens horizontally reciprocates in the radial direction of the optical disk (direction along which the turntable assembly is formed), so that the reading and reproduction of the optical disk by the optical pick-up is achieved.
Meanwhile, the distance between the object lens of the optical pick-up and the information-recording surface of the optical disk is referred to as a focal distance or working distance, and a process of adjusting the working distance is required to accurately read the information recorded on the information-recording surface. Additionally, the working distance should be differently applied according to the type of an optical disk.
For example, the CD has a structure in which a transparent substrate about 1.2 mm thick is formed on the information-recording surface thereof. In this case, the wavelength of laser light used for the CD is about 780 nm and the value of a numerical aperture NA is 0.45. The DVD has a structure in which a transparent substrate about 0.6 mm thick is formed on the information-recording surface thereof. In this case, the wavelength of laser light used for the DVD is about 650 nm and the value of a numerical aperture NA is 0.60. Additionally, the BD has a structure in which a cover layer about 0.1 mm thick is formed on the information-recording surface thereof. In this case, the wavelength of laser light used for the BD is about 400 nm and the value of a numerical aperture NA is 0.85.
As described above, the working distance between the object lens and the optical disk should be differently applied according to the types of optical disks (e.g., CD, DVD and BD). Generally, the working distance is adjusted by adjusting the posture and location of the object lens in the optical pick-up.
FIG. 1 is a view schematically showing the principal part of an optical disk device 10 according to an example of the prior art. Referring to FIG. 1, a spindle motor 40 is secured to a base 80, and a turntable 32 is mounted on the rotating shaft 42 of the spindle motor 40. Various types of optical disks 20 are placed on the turntable 32, and an optical pick-up 60 for reading information from a placed optical disk is placed on a portion of the base 80. The optical pick-up 60 can move in the radial direction of the optical disk (the direction indicated by an arrow R) below the optical disk. An actuator 66 is provided in the optical pick-up 60 and the object lens 62 is supported by wires 64 secured to the actuator 66.
The object lens 62 is constructed to move in a vertical direction (focusing direction) and a horizontal direction (tracking direction). In practice, the location of the object lens relative to the optical disk is controlled through the control of a tracking servo (not shown) and a focusing servo (not shown). In this case, the focusing servo controls the movement of the object lens in a vertical direction, so that the working distance between the object lens and the optical disk can be adjusted through the control of the focusing servo.
In the optical disk device, the working distance is adjusted by vertically moving the object lens of the optical pick-up toward the surface of the optical disk. In this case, the movement range of the object lens in which linearity is guaranteed, that is, the movable range of a focus in which the linearity is guaranteed is implemented within a range of 0.8 to 1.2 mm. However, the movement range of a focus is insufficient to allow all of the CD, the DVD and the BD to be compatible with the optical disk device, and a dual deck system, in which different decks are applied depending on optical disks, may be required to deal with all of the CD, the DVD and the BD.
Furthermore, since the optical disk device adopts a method of adjusting the working distance between the object lens and the optical disk by driving the object lens of the optical pick-up, the Direct Current (DC) sensibility (DC follow-up property) and tilt characteristics of the actuator can be considerably affected when the object lens is excessively adjusted.
Meanwhile, a turntable device capable of adjusting the working distance between an optical disk and an object lens by directly driving a turntable is disclosed in Korean Pat. No. 162416 (registered on Aug. 29, 1998). FIGS. 2a and 2b are an exploded perspective view of an optical disk device 110 and a sectional view of a turntable device 130, respectively, which are disclosed in Korean Pat. No. 162416 according to another example of the prior art.
The turntable device of FIGS. 2a and 2b includes a turntable 132, a vertical movement support unit 147 for supporting the movement of the turntable in a vertical direction, a vertical movement drive unit 151 for driving the turntable in a vertical direction, and a vertical movement control unit 159 for controlling the height of the turntable that moves in a vertical direction.
In particular, in the conventional turntable device, the vertical movement support unit 147 includes a rotating shaft support plate 146 for directly supporting the rotating shaft 142 of the turntable and an elastic member 148 for providing elastic restoring force to the rotating shaft support plate 146. The rotating shaft 142, together with surrounding rotator and stator, constitutes a spindle motor 140. The vertical movement drive unit 151 includes a vertical movement drive member 150 that is combined with a portion of the vertical movement support unit 147 using a hinge 152, and is combined with the elastic member 148 of the vertical movement support unit 147 on an inner portion thereof. The vertical movement control unit 159 includes a drive plate 156 in which a multi-stage guide slot 158 for guiding an interlock pin 154 formed at an outer end of the vertical movement drive member 150 is formed, and a drive cam 157 for driving the drive plate 156. The deck interlock pin 182 of the deck 180 is inserted into and guided by the multi-stage guide slot 158.
The operational principle of the conventional turntable device is described below. The drive plate 156 interlocked with the interlock pin 154 moves in a left direction of the drawing under the control of the vertical movement control unit 159 (refer to the rotating range of the drive cam shown in FIG. 2a). In the case where a difference in height between the interlock pin 154 and the deck interlock pin 182 occurs while the drive plate 156 moves, the vertical movement drive member 150 is rotated around the hinge 152. An end portion of the vertical movement drive member 150 is lowered by the rotation of the vertical movement drive member 150, and the vertical movement support unit 147 combined with the end portion 153 is also lowered, so that the height of the turntable is lowered.
The conventional turntable device can deal with different working distances in such a way that the height of the turntable is set based on an optical disk whose working distance is relatively short (e.g., DVD) and the height of the turntable is lowered in the case where the optical disk whose working distance is relatively long (e.g., CD) is placed. Accordingly, the conventional turntable device has a structure to which all optical disks (e.g., CD and DVD) can be applied.
However, the conventional turntable device is basically manufactured to deal with two types of optical disks, and it is difficult to apply three types of optical disks, including a BD that is recently proposed, to the conventional turntable device.
For example, in the conventional turntable device, the multi-stage guide slot 158 is formed to be divided into a first guide part 158-1, a second guide part 158-2 and a third guide part 158-3, and the posture of the deck 180 and the turntable 132 is controlled based on the relative locations of the interlock pin 154 of the vertical movement drive member 150 and the deck interlock pin 182 of the deck 180.
In practice, the posture of the deck 180 and the turntable 132 is controlled through the optical disk loading step of lowering the entire surface of the deck 180 using the rotating shaft 184 as a hinge, the first disk placing step of placing an optical disk whose focal distance is short (e.g., DVD) and the second disk placing step of placing an optical disk whose focal distance is long (e.g., CD). It is difficult to apply a third optical disk, such as a BD, to the conventional turntable device in view of the above-described structure.
Furthermore, the conventional turntable device can be basically applied to a structure in which a deck can be rotated by a hinge shaft, but cannot be applied to an optical disk device in which a deck itself is horizontally secured.
Furthermore, the conventional turntable device has a structure in which the interlock pin of the turntable (more accurately, the interlock pin of the vertical movement drive member) and the interlock pin of the deck are driven while being inserted into the multi-stage guide slot, and the relative height relationship between the deck and the turntable is used. Accordingly, it is impossible to provide a turntable device to which three types of optical disks can be applied even though a guide slot having one more stage is formed.
Furthermore, in the conventional turntable device, the control of the vertical movement of the turntable is achieved through a plurality of connection structures in which related elements are connected in the sequence of the drive cam→the drive plate→the interlock pin→the vertical movement drive member (hinge)→the rotating shaft support plate→the rotating shaft→the turntable, so that it is difficult to maintain the precision of the control.
Besides, in the case of the conventional turntable, errors may occur in the manufacture of the respective elements, and operational errors can occur as the manufacturing errors are accumulated.